Baby bottles are a unique container in that they can be processable by a variety of processes (extrusion blow molding, stretch blow molding, etc) but must be resistant to sterilization. Typically, containers are sterilized prior to use by exposure to the steam of boiling water, or by immersion in boiling water. Times of exposure can be as long as several hours. Polypropylene has been used to fabricate baby bottles, but these bottles are hazy and are not regarded as premium. Consumers desire high clarity to ensure that the milk provided to their babies is not tainted. Conventional bottles made using common clear materials, such as poly(ethylene terephthalate), will typically lose their shape during sterilization due to the low glass transition temperature of this material relative to boiling water. Thus, other materials, such as bisphenol-A polycarbonate and polysulfone are commonly used to fabricate baby bottles. However, these materials have certain deficiencies, such as cost, consumer perception, chemical resistance, hydrolytic stability, etc. which can limit their use in these applications. Thus, there is a need in the industry for a high-heat, transparent material that can be used to fabricate baby bottles that does not possess these deficiencies.
Poly(1,4-cyclohexylenedimethylene terephthalate) (PCT), a polyester based solely on terephthalic acid, an ester thereof, or mixtures thereof; and 1,4-cyclohexanedimethanol, is known in the art and is commercially available. This polyester crystallizes rapidly upon cooling from the melt, making it very difficult to form amorphous articles by methods known in the art such as extrusion, injection molding, and the like. In order to slow down the crystallization rate of PCT, copolyesters can be prepared containing additional dicarboxylic acids or glycols such as isophthalic acid or ethylene glycol. These ethylene glycol- or isophthalic acid-modified PCTs are also known in the art and are commercially available.
One common copolyester used to produce films, sheeting, and molded articles is made from terephthalic acid, 1,4-cyclohexanedimethanol, and ethylene glycol. While these copolyesters are useful in many end-use applications, they exhibit deficiencies in properties such as glass transition temperature and impact strength when sufficient modifying ethylene glycol is included in the formulation to provide for long crystallization half-times. For example, copolyesters made from terephthalic acid, 1,4-cyclohexanedimethanol, and ethylene glycol with sufficiently long crystallization half-times can provide for amorphous products that exhibit what is believed to be higher ductile-to-brittle transition temperatures and lower glass transition temperatures than the compositions revealed herein.
Polymers containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol have also been generally described in the art. Generally, however, these polymers exhibit high inherent viscosities, high melt viscosities and/or high Tgs (glass transition temperatures) such that the equipment used in industry can be insufficient to manufacture or post polymerization process these materials.
Thus, there is a need in the art for baby bottles comprising at least one polymer having a unique combination of two or more properties, chosen from the following: toughness and high glass transition temperatures, high impact strength, hydrolytic stability, chemical resistance, long crystallization half-times, low ductile to brittle transition temperatures, good color and clarity, lower density, and/or thermoformability of polyesters while retaining processability on the standard equipment used in the industry.